Star-shaped oligothiophene-arylene derivatives and organic thin film transistors using the same

ABSTRACT

A star-shaped oligothiophene-arylene derivative in which an oligothiophene having p-type semiconductor characteristics is bonded to an arylene having n-type semiconductor characteristics positioned in the central moiety of the molecule and forms a star shape with the arylene, thereby simultaneously exhibiting both p-type and n-type semiconductor characteristics. Further, an organic thin film transistor using the oligothiophene-arylene derivative. The star-shaped oligothiophene-arylene derivative can be spin-coated at room temperature, leading to the fabrication of organic thin film transistors simultaneously satisfying the requirements of high charge carrier mobility and low off-state leakage current.

This non-provisional application claims priority under 35 U.S.C. §119(a) on Korean Patent Application No. 2004-98674 filed on Nov. 29, 2004, which is herein expressly incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a star-shaped oligothiophene-arylene derivative and an organic thin film transistor using the derivative. More particularly, the present invention relates to a star-shaped oligothiophene-arylene derivative in which an oligothiophene having p-type semiconductor characteristics is bonded to an arylene having n-type semiconductor characteristics positioned in the central moiety of the molecule and forms a star shape with the arylene, thereby simultaneously exhibiting both p-type and n-type semiconductor characteristics.

2. Description of the Related Art

General organic thin film transistors (OTFTs) comprise a substrate, a gate electrode, an insulating layer, source/drain electrodes, and a channel layer. Organic thin film transistors are classified into bottom-contact (BC) OTFTs wherein a channel layer is formed on source and drain electrodes, and top-contact (TC) OTFTs wherein metal electrodes are formed on a channel layer by mask deposition.

Inorganic semiconductor materials, such as silicon (Si), have been commonly used as materials for channel layers of OTFTs. However, since the preparation of such inorganic semiconductor materials involves high costs and requires a high-temperature vacuum process to fabricate OTFTs, organic semiconductor materials are currently replacing inorganic semiconductor materials in order to fabricate large area, flexible displays at reduced costs.

Recently, studies on organic semiconductor materials for channel layers of OTFTs have been actively undertaken and the characteristics of the devices have been reported. Of these, a great deal of research is currently concentrated on low molecular weight materials and oligomers, e.g., melocyanines, phthalocyanines, perylenes, pentacenes, C60, thiophene oligomers, and the like. Lucent Technologies Inc. and 3M Inc. developed devices with charge carrier mobilities as high as 3.2-5.0 cm²/Vs using a pentacene single crystal (Mat. Res. Soc. Symp. Proc. 2003, Vol. 771, L6.5.1-L6.5.11). In addition, CNRS, France, reported a device having a relatively high charge carrier mobility of 0.01-0.1 cm²/Vs and a relatively high on/off current ratio (I_(on)/I_(off) ratio) using an oligothiophene derivative (J. Am. Chem. Soc., 1993, Vol. 115, pp. 8716-9721).

However, since the prior art devices are largely dependent on vacuum processes for thin film formation, the fabrication of the devices incurs considerable costs.

On the other hand, high molecular weight-based organic thin film transistors (charge carrier mobility: 0.01-0.02 cm²/Vs) employing a polythiophene-based material (F8T2) have already been fabricated and tested (PCT Publication WO 00/79617, Science, 2000, vol. 290, pp. 2132-2126). U.S. Pat. No. 6,107,117 discloses the fabrication of an organic thin film transistor with a charge carrier mobility of 0.01-0.04 cm²/Vs by employing polythiophene P3HT, which is a representative regioregular polymer.

Since the regioregular polythiophene P3H5 shows a charge carrier mobility of about 0.01 cm²/Vs but a high off-state leakage current (10⁻⁹A or more), leading to a low I_(on)/I_(off) ratio of 400 or less, it is not applicable to the fabrication of electronic devices.

Low molecular weight organic semiconductor materials for organic thin film transistors that can be spin-coated at room temperature and simultaneously satisfy the requirements of high charge carrier mobility and low off-state leakage current, have not hitherto been reported.

OBJECTS AND SUMMARY

Therefore, embodiments of the present invention have been made to satisfy the above-mentioned need in the art to which the present invention pertains. It is an object of the embodiments of the present invention to provide a star-shaped oligothiophene-arylene derivative in which an oligothiophene having p-type semiconductor characteristics is bonded to an arylene having n-type semiconductor characteristics positioned in the central moiety of the molecule and forms a star shape with the arylene, thereby enabling spin-coating at room temperature and simultaneously exhibiting both high charge carrier mobility and low leakage current.

In accordance with one aspect of the present invention, there is provided a star-shaped oligothiophene-arylene derivative represented by Formula 1 below:

wherein

Ar is a C₂₋₃₀ arylene interrupted by at least one nitrogen atom which may be substituted with hydrogen, hydroxyl, amine, C₁₋₂₀ linear, branched or cyclic alkyl, alkoxy, C₁₋₂₀ alkoxyalkyl, alkylamine, ester or amide;

Ar₁ is a C₂₋₃₀ aryl group which may be interrupted by at least one heteroatom and may be substituted with hydrogen, hydroxyl, amine, C₁₋₂₀ linear, branched or cyclic alkyl, alkoxy, C₁₋₂₀ alkoxyalkyl, alkylamine, ester or amide;

Ar₂ is a C₅₋₃₀ aryl group which may be interrupted by at least one heteroatom and may be substituted with hydrogen, hydroxyl, amine, C₁₋₂₀ linear, branched or cyclic alkyl, alkoxy, C₁₋₂₀ alkoxyalkyl, alkylamine, ester or amide; the substituents R are independently hydrogen, hydroxyl, amine, C₁₋₂₀ linear, branched or cyclic alkyl, alkoxy, C₁₋₂₀ alkoxyalkyl, alkylamine, ester or amide;

n is an integer between 3 and 8;

n₁ and n₃ are each independently an integer between 0 and 6; and

n₂ is an integer between 2 and 8.

In accordance with another aspect of the present invention, there is provided a method for preparing the star-shaped oligothiophene-arylene derivative.

In accordance with yet another aspect of the embodiments of the present invention, there is provided an organic thin film transistor in which the single molecular compound is used as a material for an organic active layer, thereby enabling spin-coating at room temperature and simultaneously satisfying the requirements of high charge carrier mobility and low off-state leakage current.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a cross-sectional view showing the structure of an organic thin film transistor fabricated in Example 1 of the present invention;

FIG. 2 is a ¹H-NMR spectrum of an oligothiophene-arylene derivative prepared in Preparative Example 3 of the present invention; and

FIG. 3 is a graph showing the current transfer characteristics of an organic thin film transistor fabricated in Example 1 of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the embodiments of the present invention will be described in detail.

The embodiments of the present invention provide a star-shaped oligothiophene-arylene derivative in which an oligothiophene having p-type semiconductor characteristics is bonded to an arylene having n-type semiconductor characteristics positioned in the central moiety of the molecule and forms a star shape with the arylene.

The star-shaped oligothiophene-arylene derivative is represented by Formula 1 below:

wherein

Ar is a C₂₋₃₀ arylene interrupted by at least one nitrogen atom which may be substituted with hydrogen, hydroxyl, amine, C₁₋₂₀ linear, branched or cyclic alkyl, alkoxy, C₁₋₂₀ alkoxyalkyl, alkylamine, ester or amide;

Ar₁ is a C₂₋₃₀ aryl group which may be interrupted by at least one heteroatom and may be substituted with hydrogen, hydroxyl, amine, C₁₋₂₀ linear, branched or cyclic alkyl, alkoxy, C₁₋₂₀ alkoxyalkyl, alkylamine, ester or amide;

Ar₂ is a C₅₋₃₀ aryl group which may be interrupted by at least one heteroatom and may be substituted with hydrogen, hydroxyl, amine, C₁₋₂₀ linear, branched or cyclic alkyl, alkoxy, C₁₋₂₀ alkoxyalkyl, alkylamine, ester or amide;

the substituents R are independently hydrogen, hydroxyl, amine, C₁₋₂₀ linear, branched or cyclic alkyl, alkoxy, C₁₋₂₀ alkoxyalkyl, alkylamine, ester or amide;

n is an integer between 3 and 8;

n₁ and n₃ are each independently an integer between 0 and 6; and

n₂ is an integer between 2 and 8.

In the star-shaped oligothiophene-arylene derivative of Formula 1 according to the embodiments of the present invention, non-limiting representative examples of compounds corresponding to Ar include compounds represented by Formula 2 below:

wherein

R₁ to R₄ are independently hydrogen, hydroxyl, amine, C₁₋₂₀ linear, branched or cyclic alkyl, alkoxy, C₁₋₂₀ alkoxyalkyl, alkylamine, ester or amide.

Specific examples of the compounds of Formula 2 include, but are not limited to, thiadiazoles, oxazoles, isoxazoles, oxadiazoles, imidazoles, pyrazoles, thiadiazoles, triazoles, tetrazoles, pyridines, pyridazines, pyrimidines, pyrazines, triazines, quinolines, isoquinolines, quinoxalines, naphthyridines, benzoimidazoles, pyrimidopyrimidines, benzothiadiazoles, benzoselenadiazoles, benzotriazoles, benzothiazoles, benzoxazoles, phenanthrolines, phenazines, and phenanthridines.

In the star-shaped oligothiophene-arylene derivative of Formula 1 according to the embodiments of the present invention, non-limiting representative examples of compounds corresponding to Ar₁ include compounds represented by Formula 3 below:

wherein

R₅ to R₁₃ are independently hydrogen, hydroxyl, amine, C₁₋₂₀ linear, branched or cyclic alkyl, alkoxy, C₁₋₂₀ alkoxyalkyl, alkylamine, ester or amide.

Specific examples of the compounds of Formula 3 include, but are not limited to, thiophenes, thiazoles, thiadiazoles, oxazoles, isoxazoles, oxadiazoles, imidazoles, pyrazoles, thiadiazoles, triazoles, tetrazoles, pyridines, pyridazines, pyrimidines, pyrazines, triazines, quinolines, isoquinolines, quinoxalines, naphthyridines, benzoimidazoles, pyrimidopyrimidines, benzothiadiazoles, benzoselenadiazoles, benzotriazoles, benzothiazoles, benzoxazoles, phenanthrolines, phenazines, phenanthridines, benzenes, naphthalenes, and fluorenes.

In the star-shaped oligothiophene-arylene derivative of Formula 1 according to the present invention, non-limiting representative examples of compounds corresponding to Ar₂ include compounds represented by Formula 4 below:

wherein

R₁₄ to R₂₁ are independently hydrogen, hydroxyl, amine, C₁₋₂₀ linear, branched or cyclic alkyl, alkoxy, C₁₋₂₀ alkoxyalkyl, alkylamine, ester or amide.

Specific examples of the compounds of Formula 4 include, but are not limited to, C₅₋₃₀ aromatic compounds, for example, benzenes, naphthalenes, anthracenes, and fluorenes.

The star-shaped oligothiophene-arylene derivative of the embodiments of the present invention can be synthesized by chemical or electrochemical oxidation and condensation using an organometallic compound of a transition metal, such as nickel or palladium, which are representative polymerization processes of heteroaromatic compounds.

That is, the star-shaped oligothiophene-arylene derivative of the embodiments of the present invention is synthesized by polymerizing compounds of Formulae 5 to 8 below:

ArX₁)_(m)  Formula 5

wherein Ar is as defined in Formula 1, X₁ is Br, Cl, or I, and m is an integer between 3 and 8;

wherein Ar₁ is as defined in Formula 1, X₂ is a trialkyltin group, a dioxaborane group, or boronic acid, and n₁ is an integer between 0 and 6;

wherein R is as defined in Formula 1, X₃ is a trialkyltin group, a dioxaborane group, or boronic acid, and n₂ is an integer between 2 and 8; and

wherein Ar₂ is as defined in Formula 1, X₄ is a trialkyltin group, a dioxaborane group, or boronic acid, and n₃ is an integer between 0 and 6, at 70-130° C. in the presence of at least one catalyst represented by Formulae 9 to 11 below:

PdL₄  Formula 9

wherein L is a ligand selected from the group consisting of triphenylphosphine (PPh₃), triphenylarsine (AsPh₃), triphenylphosphite (P(OPh)₃), diphenylphosphinoferrocene (dppf), diphenylphosphino butane (dppb), acetate (OAc), and dibenzylideneacetone (dba);

PdL₂X₂  Formula 10

wherein L is as defined in Formula 9, and X is I, Br or Cl; and

PdL₂  Formula 11

wherein L is as defined in Formula 9.

Specifically, the star-shaped oligothiophene-arylene derivative of the embodiments of the present invention is synthesized through the reaction paths depicted by the following Reaction Scheme 1:

The star-shaped oligothiophene-arylene derivative is synthesized by the Suzuki coupling reaction. One example of a star-shaped oligothiophene-arylene derivative that can be synthesized by the Suzuki coupling reaction is the compound represented by Formula 12 below:

Halide-substituted arylene derivatives (e.g., the compound of Formula 5) and boron-substituted compounds (e.g., the compounds of Formulae 6 to 8) are used to synthesize the star-shaped oligothiophene-arylene derivative of Formula 12. Compounds used to prepare the oligothiophene-arylene derivative of Formula 12, an embodiment of the present invention, are those represented by Formulae 13 and 14 below:

The star-shaped oligothiophene-arylene derivative of the embodiments of the present invention can be used as a novel organic semiconductor material for an active layer of an OTFT. General organic thin film transistors have structures of a substrate/a gate electrode/a gate insulating layer/an organic active layer/source-drain electrodes, a substrate/a gate electrode/a gate insulating layer/source-drain electrodes/an organic active layer, and the like, but are not limited to these structures.

At this time, the star-shaped oligothiophene-arylene derivative of the embodiments of the present invention can be formed into a thin film by, for example, screen printing, printing, spin coating, dipping, or ink spraying.

The gate insulating layer constituting the OTFT can be made of common high-dielectric constant insulators. Specific examples of suitable insulators include, but are not limited to, ferroelectric insulators, e.g., Ba_(0.33)Sr_(0.66)TiO₃ (BST), Al₂O₃, Ta₂O₅, La₂O₅, Y₂O₃, and TiO₂; inorganic insulators, e.g., PbZr_(0.33)Ti_(0.66)O₃ (PZT), Bi₄Ti₃O₁₂, BaMgF₄, SrBi₂(TaNb)₂O₉, Ba(ZrTi)O₃ (BZT), BaTiO₃, SrTiO₃, Bi₄Ti₃O₁₂, SiO₂, SiN_(x), and AlON; and organic insulators, e.g., polyirpides, benzocyclobutenes (BCBs), parylenes, polyacrylates, polyvinylalcohols, polyvinylphenols, and the like.

The substrate can be made of, but is not limited to, glass, polyethylenenaphthalate (PEN), polyethyleneterephthalate (PET), polycarbonate, polyvinylalcohol, polyacrylate, polyimide, polynorbornene, polyethersulfone (PES), and the like.

The gate electrode and source-drain electrodes can be made of common metals. Specific examples of such metals include, but are not limited to, gold (Au), silver (Ag), aluminum (Al), nickel (Ni), indium tin oxide (ITO), and molybdenum/tungsten (Mo/W).

Embodiments of the present invention will now be described in more detail with reference to the following examples. However, these examples are given for the purpose of illustration and are not to be construed as limiting the scope of the invention.

Preparative Example 1 Preparation of Oligothiophene Borolanes 1 and 2

n-BuLi in tetrahydrofuran (THF) was added to 3-hexyl thiophene at −20° C., and then N,N,N′,N′-tetramethylethylenediamine (TMEDA) was added thereto. The mixture was heated to 70° C. for 3 hours. Subsequently, dioxaborolane was added to the mixture at −78° C. and was slowly allowed to warm to room temperature to obtain the oligothiophene borolane 1.

The oligothiophene borolane 1 and 2-bromothiophene were added to a mixture of toluene and water, and then tetrakis(triphenylphosphine)palladium (0) (Pd(PPh₃)₄, Aldrich) as a catalyst and potassium carbonate were added thereto. The reaction mixture was allowed to react at 110° C. for 8 hours to obtain the compound 2a.

n-BuLi in tetrahydrofuran was added to the compound 2a at −20° C., and then N,N,N′,N′-tetramethylethylenediamine (TMEDA) was added thereto. The mixture was heated to 70° C. for 3 hours. Subsequently, dioxaborolane was added to the mixture at −78° C. and was slowly allowed to warm to room temperature to afford the oligothiophene borolane 2.

¹H-NMR (300 MHz, CDCl₃) δ (ppm) 0.89 (t, 3H, J=6.8 Hz), 6H), 1.21-1.35 (m, 18H), 1.59-1.66 (m, 2H), 2.58 (t, 2H, J=7.8 Hz), 6.68 (s, 1H), 7.00 (s, 1H), 7.20 (d, 1H, J=3.5 Hz), 7.47 (d, 1H, J=3.5 Hz)

Preparative Example 2 Preparation of Oligothiophene Borolanes 3 and 4

Thiophen-2-yl-magnesium bromide was added to a mixture of hexanal and THF to obtain the compound 3a. Zinc iodide, sodium cyanoborohydride and 1,2-dichloroethane were added to the compound 3a, and then the mixture was heated to 85° C. for 3 hours to obtain the compound 3b. Lithium diisopropylamide (LDA) in THF was added to the compound 3b at −78° C., and then dioxaborolane was added thereto to obtain the thiophene borolane 3. Thereafter, the thiophene borolane 3 and 2-bromobithiophene were reacted under the same conditions as in the preparation of the compound 2a indicated in Preparative Example 1 to obtain the compound 4a. Lithium diisopropylamide (LDA) in THF was added to the compound 4a at −78° C., and then dioxaborolane was added thereto to afford the oligothiophene borolane 4.

¹H-NMR (300 MHz, CDCl₃) δ (ppm) 0.89 (t, 3H, J=6.8 Hz), 1.25-1.43 (m, 18H), 1.60-1.75 (m, 2H), 2.78 (t, 2H, J=7.5 Hz), 6.65 (d, 1H, J=3.5 Hz), 7.04 (d, 1H, J=3.5 Hz), 7.15 (d, 1H, J=3.5 Hz), 7.49 (d, 1H, J=3.5 Hz)

Preparative Example 3 Preparation of Oligothiophene-Arylene Derivative 1

2,4,6,8-Tetrachloro-pyrimido[5,4-d]pyrimidine (TCI) and the oligothiophene borolane 2 were subjected to condensation by the Suzuki coupling reaction to obtain the compound 1a. To the compound 1a was added N-bromosuccinimide (NBS) in chloroform to obtain the dibromide 1b. The dibromide 1b and the oligothiophene borolane 4 were mixed with toluene and water, and then Pd(PPh₃)₄ as a catalyst and potassium carbonate in a solvent were added thereto. The resulting mixture was heated to 110° C. for 8 hours and washed with an aqueous ammonium chloride solution. The obtained organic layer was distilled under reduced pressure and purified by silica gel column chromatography, affording the derivative 1.

¹H-NMR (300 MHz, CDCl₃) δ (ppm) 0.85-0.94 (m, 24H), 1.29-1.42 (m, 48H), 1.56-1.63 (m, 8H), 1.63-1.76 (m, 8H), 2.53-2.65 (m, 8H), 2.73-2.81 (m, 8H), 6.50-6.60 (m, 4H), 6.81-6.90 (m, 20H), 7.52 (s, 2H), 8.28 (s, 2H)

Fabrication of OTFTs Example 1 Fabrication of Organic Thin Film Transistor Using Oligothiophene-Arylene Derivative 1

First, molybdenum/tungsten (Mo/W) were deposited on a glass substrate that had been previously washed by a sputtering process to form a gate electrode having a thickness of 1,000 Å. Thereafter, a polyacrylate-based polymer was deposited on the gate electrode by a spin-coating process to form a gate insulating film, and was then dried at 150° C. for one hour. Gold (Au) as a material for source-drain electrodes was deposited on the gate insulating layer to a thickness of 500 Å by a sputtering process. Separately, the oligothiophene-arylene derivative 1 prepared in Preparative Example 3 was dissolved in toluene to obtain a 2 wt % solution. The solution was applied to the resulting structure at 1,000 rpm to a thickness of 800 Å, and baked at 100° C. for one hour to fabricate an OTFT as schematically illustrated in FIG. 1.

Comparative Example 1

An organic thin film transistor was fabricated in the same manner as in Example 1, except that polyhexylthiophene HT-P3HT (Aldrich) was used.

Evaluation of Electrical Properties of OTFTs

The charge carrier mobility of the devices fabricated in Example 1 and Comparative Example 1 was measured. The current transfer characteristics of the devices were evaluated using a KEITHLEY semiconductor characterization system (4200-SCS), and curves were plotted. The obtained results are shown in Table 1. The charge carrier mobility was calculated using the curve from the following current equations in the saturation region.

The charge carrier mobility was calculated from the slope of a graph representing the relationship between (I_(SD))^(1/2) and V_(G) from the following current equations in the saturation region:

$I_{SD} = {\frac{{WC}_{0}}{2L}{\mu \left( {V_{G} - V_{T}} \right)}^{2}}$ $\sqrt{I_{SD}} = {\sqrt{\frac{\mu \; C_{0}W}{2L}}\left( {V_{G} - V_{T}} \right)}$ ${slope} = \sqrt{\frac{\mu \; C_{0}W}{2L}}$ $\mu_{FET} = {({slope})^{2}\frac{2L}{C_{0}W}}$

In the above equations, I_(SD): source-drain current, μ and μ_(FET): charge carrier mobility, C_(o): capacitance of the oxide film, W: channel width, L: channel length; V_(G): gate voltage, and V_(T): threshold voltage.

Off-state leakage current (I_(off)) is a current flowing in the off-state, and was determined from the minimum current in the off-state.

TABLE 1 Charge carrier mobility Off-state leakage Organic active layer (cm²/Vs) current (A) Example 1 0.00005 1 × 10⁻¹² Comparative Example 1 0.01 1 × 10⁻⁸  (HT-P3HT)

As can be seen from the data shown in Table 1, the oligothiophene-arylene derivatives of the present invention showed a considerably low off-state leakage current of 1×10⁻¹² A and a high charge carrier mobility of 0.00005.

As apparent from the foregoing, the star-shaped oligothiophene-arylene derivative of the present invention is a low-molecular weight organic semiconductor material with a novel structure. In addition, since the oligothiophene-arylene derivative can be spin-coated at room temperature, is stable, and exhibits low off-state leakage current, it can be used as a material for an active layer of an OTFT.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. 

1. A star-shaped oligothiophene-arylene derivative comprising an oligothiophene having p-type semiconductor characteristics bonded to an arylene having n-type semiconductor characteristics positioned in a central moiety of a derivative molecule to form a star shape with the arylene, represented by Formula 1 below:

wherein Ar is a C₂₋₃₀ arylene interrupted by at least one nitrogen atom which may be substituted with hydrogen, hydroxyl, amine, C₁₋₂₀ linear, branched or cyclic alkyl, alkoxy, C₁₋₂₀ alkoxyalkyl, alkylamine, ester or amide; Ar₁ is a C₂₋₃₀ aryl group which may be interrupted by at least one heteroatom and may be substituted with hydrogen, hydroxyl, amine, C₁₋₂₀ linear, branched or cyclic alkyl, alkoxy, C₁₋₂₀ alkoxyalkyl, alkylamine, ester or amide; Ar₂ is a C₅₋₃₀ aryl group which may be interrupted by at least one heteroatom and may be substituted with hydrogen, hydroxyl, amine, C₁₋₂₀ linear, branched or cyclic alkyl, alkoxy, C₁₋₂₀ alkoxyalkyl, alkylamine, ester or amide; R is hydrogen, hydroxyl, amine, C₁₋₂₀ linear, branched or cyclic alkyl, alkoxy, C₁₋₂₀ alkoxyalkyl, alkylamine, ester or amide; n is an integer between 3 and 8; n₁ and n₃ are each independently an integer between 0 and 6; and n₂ is an integer between 2 and
 8. 2. The star-shaped oligothiophene-arylene derivative according to claim 1, wherein Ar is selected from the group consisting of compounds represented by Formula 2 below:

wherein R₁, R₂, R₃, and R₄ are independently hydrogen, hydroxyl, amine, C₁₋₂₀ linear, branched or cyclic alkyl, alkoxy, C₁₋₂₀ alkoxyalkyl, alkylamine, ester or amide.
 3. The star-shaped oligothiophene-arylene derivative according to claim 1, wherein Ar₁ is selected from the group consisting of compounds represented by Formula 3 below:

wherein R₅, R₆, R₇, R₈, R₉, R₁₀, R₁₁, R₁₂, R₁₃ are independently hydrogen, hydroxyl, amine, C₁₋₂₀ linear, branched or cyclic alkyl, alkoxy, C₁₋₂₀ alkoxyalkyl, alkylamine, ester or amide.
 4. The star-shaped oligothiophene-arylene derivative according to claim 1, wherein Ar₂ is selected from the group consisting of compounds represented by Formula 4 below:

wherein R₁₄, R₁₅, R₁₆, R₁₇, R₁₈, R₁₉, R₂₀, R₂₁ are independently hydrogen, hydroxyl, amine, C₁₋₂₀ linear, branched or cyclic alkyl, alkoxy, C₁₋₂₀ alkoxyalkyl, alkylamine, ester or amide.
 5. A method for preparing a star-shaped oligothiophene-arylene derivative comprising polymerizing compounds represented by Formulae 5, 6, 7 and 8 below: ArX₁)_(m)  (5) wherein Ar is a C₂₋₃₀ arylene interrupted by at least one nitrogen atom which may be substituted with hydrogen, hydroxyl, amine, C₁₋₂₀ linear, branched or cyclic alkyl, alkoxy, C₁₋₂₀ alkoxyalkyl, alkylamine, ester or amide, X₁ is Br, Cl, or I, and m is an integer between 3 and 8;

wherein Ar₁ is a C₂₋₃₀ aryl group which may be interrupted by at least one heteroatom and may be substituted with hydrogen, hydroxyl, amine, C₁₋₂₀ linear, branched or cyclic alkyl, alkoxy, C₁₋₂₀ alkoxyalkyl, alkylamine, ester or amide, X₂ is a trialkyltin group, a dioxaborane group, or boronic acid, and n₁ is an integer between 0 and 6;

wherein R is hydrogen, hydroxyl, amine, C₁₋₂₀ linear, branched or cyclic alkyl, alkoxy, C₁₋₂₀ alkoxyalkyl, alkylamine, ester or amide, X₃ is a trialkyltin group, a dioxaborane group, or boronic acid, and n₂ is an integer between 2 and 8; and

wherein Ar₂ is a C₅₋₃₀ aryl group which may be interrupted by at least one heteroatom and may be substituted with hydrogen, hydroxyl, amine, C₁₋₂₀ linear, branched or cyclic alkyl, alkoxy, C₁₋₂₀ alkoxyalkyl, alkylamine, ester or amide, X₄ is a trialkyltin group, a dioxaborane group, or boronic acid, and n₃ is an integer between 0 and 6, at 70-130° C. in the presence of at least one catalyst represented by Formulae 9, 10, and 11 below: PdL₄  (9) wherein L is a ligand selected from the group consisting of triphenylphosphine, triphenylarsine, triphenylphosphite, diphenylphosphinoferrocene, diphenylphosphino butane, acetate, and dibenzylideneacetone; PdL₂X₂  (10) wherein L is as defined in Formula 9, and X is I, Br or Cl; and PdL₂  (11) wherein L is as defined in Formula
 9. 6. An organic thin film transistor comprising a substrate, a gate electrode, a gate insulating layer, an organic active layer and source-drain electrodes wherein the organic active layer is made of the star-shaped oligothiophene-arylene derivative according to claim
 1. 7. The organic thin film transistor according to claim 6, wherein the organic active layer is formed into a thin film by screen printing, printing, spin coating, dipping, or ink spraying.
 8. The organic thin film transistor according to claim 6, wherein the gate insulating layer is made of a ferroelectric insulator selected from the group consisting of Ba_(0.33)Sr_(0.66)TiO₃, Al₂O₃, Ta₂O₅, La₂O₅, Y₂O₃, and TiO₂; an inorganic insulator selected from the group consisting of PbZr_(0.33)Ti_(0.66)O₃, Bi₄Ti₃O₁₂, BaMgF₄, SrBi₂(TaNb)₂O₉, Ba(ZrTi)O₃, BaTiO₃, SrTiO₃, Bi₄Ti₃O₁₂, SiO₂, SiN_(x), and AlON; or an organic insulator selected from the group consisting of polyimides, benzocyclobutenes, parylenes, polyacrylates, polyvinylalcohols, and polyvinylphenols.
 9. The organic thin film transistor according to claim 6, wherein the substrate is made of a material selected from the group consisting of glass, polyethylenenaphthalate, polyethyleneterephthalate, polycarbonate, polyvinylalcohol, polyacrylate, polyimide, polynorbornene, and polyethersulfone.
 10. The organic thin film transistor according to claim 6, wherein the gate electrode and source-drain electrodes are independently made of a material selected from the group consisting of gold, silver, aluminum, nickel, indium tin oxide, and molybdenum/tungsten. 